ABSTRACT
To identify the specificity of base substitutions, a novel experimental system was established based on rifampicin-resistant (Rif r) mutant screening and sequencing of the defined region of the rpoB gene in E. coli. We focused on comparing mutational spectra of base substitutions induced by either low energy nitrogen ion beam implantation or 60Co-gamma rays. The most significant difference in the frequency of specific kinds of mutations induced by low energy nitrogen ion beam was that CG -> TA transitions were significantly increased from 32 to 46, AT -> TA transversions were doubled from 7 to 15 in 50 mutants, respectively. The preferential base substitutions induced by nitrogen ion beam implantation were CG -> TA transitions, AT -> GC transitions, AT -> TA transversions, which account for 92.13 percent (82/89) of the total. The mutations induced by 60Co-gamma rays were preferentially GC -> AT and AT -> GC transitions, which totaled 84.31 percent (43/51).